Electron Transfer through Thin Organic Films and Highly Curved Donor- Bridge-Acceptor Molecules

Electron-transfer rate constants were measured for a variety of molecular systems. The rate constant was found to depend upon the nature of the medium between the electron donor and acceptor moieties. Using a superexchange model to calculate the electronic coupling between donor and acceptor, the effect of orbital energetics was studied. For photoinduced electron transfer, aromatic moieties with large electron affinities promote large electronic coupling magnitudes. In the electrochemical systems studied involving a gold electrode and an immobilized ferrocene tethered alkanethiol, alkane chains were found to be more efficient at promoting electron transfer than chains incorporating ether linkages. This indicates a dominant hole-transfer mechanism for the electrochemical systems. Chemical modification of adjacent diluent alkanethiols also resulted in alteration of the rate constant. This suggests intermolecular interactions are important in electron transfer in these systems.